Interesting question. I had to do some research to give you an answer.
A Pooled Quota Waiting List ('PQWL') is shared by several small stations in a particular region. E.g., Tiruppur, Salem, etc., share in the quota and wait list for some trains originating from Trivandrum or Mangalore. As another example, the 2723 Andhra Pradesh Exp. has three quotas, for Secunderabad - New Delhi, Secunderabad - nagpur, and Secunderabad - Bhopal. There is also a pooled quota for passengers travelling from Secunderabad to stations beyond Bhopal but short of Jhansi; if this quota is exhausted, a passenger is placed in the pooled quota waiting list. Such remote location quotas are also provided when there is a very strong demand for the train in question, because of which, without such additional quotas, all seats or berths might be fully consumed by passengers from the originating station leaving nothing available for those wishing to travel from intermediate points.
Hope this helps and I get my 10 points.